As a method of measuring a thickness of an article having a predetermined X-ray absorption coefficient in a nondestructive manner, there is a method which includes irradiating X-rays to the article, measuring a transmission amount of X-rays passed through the article, and measuring a thickness of the article based on the transmission amount and the absorption coefficient.
In general, an article to be tested is provided with members made of various substances so that X-rays pass through the members along a path defined in the article. This makes it difficult to measure only a thickness of a member made of a certain substance inside the article.
In recent years, an article such as an electronic substrate, a wafer and the like, has a structure in which members formed of various substances are stacked in plural layers. In this case, the measurement of a thickness of each member placed within the article requires preparing a slice of the article as a specimen and observing a cross-section of the specimen with an optical microscope or an electron microscope. However, the preparation and the observation of the specimen from pre-shipment goods, e.g., a semiconductor chip, a printed substrate, a battery and the like, entails significant loss in terms of time and cost. Thus, a method of testing an article in a nondestructive manner has been in demand.
However, a conventional testing method using X-rays requires a reference specimen as described above. In addition, the testing method requires a technique for accurately irradiating the X-rays to the specimen based on design diagrams of the semiconductor chip, the printed substrate, the battery and the like, while such a technique has not been developed. This makes it difficult to enhance throughput of testing.